text:
What are the various thrust modes in the Airbus A320?
I was going through A320 AFM and came across Thrust modes. I was not able to understand why thrust is in thrust mode during climb and descent because we climb or descent with a constant speed. So according to me it should be in constant speed mode.

A normal climb is performed with a constant thrust1 and a constant speed. The autothrust system will take care of the constant thrust (THR CLB) and the autopilot (or flight director for manual flight) will take care of the constant speed. This means you maintain the target speed by pitching up or down. If the speed is below target, pitch down to increase speed, and vice versa.
The same is true during a descent. The autothrust will maintain idle thrust (THR IDLE) and the autopilot or flight director will maintain the target speed by pitching down.
During cruise, where the altitude remains constant, the target speed needs to be achieved by setting the correct amount of thrust. Now the autothrust system is responsible for maintaining speed and will show SPEED or MACH on the FMA (Flight Mode Annunciator).

The A/THR modes are selected automatically in conjunction with the AP/FD modes (except ALPHA FLOOR).

(Airbus A320 FCOM - Autoflight - Flight Guidance - A/THR Modes)

1The actual thrust produced by the engine is not constant, it depends on altitude. The FADEC will compute a thrust rating limit depending on the selected thrust lever position:

The FADEC computes the thrust rating limit for each thrust lever position [...]. If the thrust lever is set in a detent, the FADEC selects the rating limit corresponding to this detent.

(Airbus A320 FCOM - Powerplant - Thrust Control System - Thrust Rating Limit)

@ymb1 Thanks, I added an explanation. Technically, speed is also not constant, as the target speed changes several times during the climb, but for any particular section, this should be fine.

Why is a descent automatically made with idle thrust?

@Vikki-formerlySean Why not? An idle descent profile gives best fuel economy by staying at high altitudes for as long as possible. When altitude or speed constraints dictate a different descent path later, the aircraft will switch to geometric path mode (see table) to meet all constraints.


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What is the purpose of the leaf spring in an altimeter?
What is the use of the leaf spring present around the partially evacuated aneroid capsule of sensitive altimeter.

The function of the spring is to pull on the evacuated capsule, such that it has a volume. Without the spring, the evacuated capsule would be entirely flat.
If the capsule were flat, a change in ambient pressure would not change the shape of the capsule; at any non-zero ambient pressure, the evacuated capsule would remain flat due to the force of the air pressure squeezing it.
Because the spring creates a force balance between the vacuum capsule and the ambient air pressure, the capsule will have a volume. Now a change in ambient pressure will change the balance between the force pulling on the capsule and the pressure of the ambient air trying to collapse it.
A new balance will be found at a different position of the spring. This change of position is translated into a rotation of the needle of the altimeter.
If the capsule was not filled with vacuum, it would expand if the temperature of the air inside it would rise, resulting in erroneous reading. With a vacuum capsule, the capsule is less sensitive to changes in temperature.
Since the capsule is made of metal, temperature has an effect on the elasticity, and thus on the balance with the spring. To compensate for this, the spring is made of bimetal. This balances out the changes of elasticity of the capsule when the temperature changes.

References:

aviationknowledge.wikidot.com
Aircraft Instruments & Integrated Systems, E.H.J. Pallett, Pearson Education Limited, 1992

So you mean to say capsule is completely vacuum from inside.  Then how does it expand as we go up .

Sir second doubt is as you are saying that spring pull up the capsule so if we go to a airfield below MSL. Then this will create huge errors.

@SourabhJain It expands because the spring is pulling. As the pressure on the capsule decreases, the spring expands it further until a new equilibrium is reached. W.r.t. going below sea level, there is no difference to the system. The pressure increases, so the balance is found with the spring more compressed.

Without the spring, the capsule would tend to collapse at or below sea-level pressure-altitude. The spring opposes the high pressure.

Source
A variation of the principle above it to put the spring on the index mechanism.

so what happens at high pressure ? does spring completely block all the static pressure going towards aneroid capsule. I am not able to get that part  and secondly what is there inside the capsule . Is there a gas or what

@SourabhJain: In the capsule there is a bit of dry air, but at very low pressure, so it easy to change its shape, a small atmospheric pressure variation is enough. Without the spring the capsule would totally collapse and its shape could therefore not vary. The spring just establishes a new equilibrium shape, but the sensitivity to pressure is still high.

So it's like spring is pulling the aneroid capsule right. Can you please share me the link from where did you learn about this.

@SourabhJain: For example, or this one. Yes it pulls on the capsules.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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What is the airfoil used in the SB13 flying wing?

(Source)
What airfoil is used for the wing of this aircraft?

According to the Wikipedia Page on SB-13 Arcus, the airfoil used are,

HQ 34N/14.83 at root, HQ 36N/15.12 at tip. Winglet Wortmann FX 7-L-150/K30

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is this Perspex bubble?
Found this during a garden clearance. Have included a photo of serial number. Could you identify where this came from?

dimensions: width 115cm length 140cm.

Do you have any further details? Which country, area (perhaps nearby air bases etc.)?

Welcome to Aviation.SE could you clarify what you want us to identify? I am thinking of type of aircraft but I do not know what you are looking for.

Has two circular holes approx 10cm diameter at end opposite hinges. Label states MODS and serial number. Its in Essex now, but think it was transported here. Keen to find out what aircraft and what it is.

Could you please re-do the first photo trying to avoid all that blurring/noise? use a camera, not a phone, and try to have better lighting conditions. thank you

Could you please add the dimensions?

Have some other photos but site wont let me add any more.

have serial number etc but blurred as perspex milky. Mentions MODS? The base is flat so could that even be for an aircraft?. Dimensions approx110cm x130cm.

@mike Would you like me to add the photos and information from your most recent question to this question?

I've added the photos you posted in you other question, but 1. I do not see the resemblance 2. the new photos are reeeeeally tiny

Are the two new pictures of the same canopy? The shapes of the objects in the two middle pictures look very, very different. Where, on the 3rd picture, are the latches visible in the 2nd picture? Maybe try some pictures against an uncluttered background, like a tarp or a driveway - something that would help eliminate background distractions.

Few thoughts:

Label font does look British/Commonwealth in some way.
Flat bottom- unlikely to be cockpit canopy that curve down on the sides.
Not compatible with weapons- Search and Rescue aircraft?
Large curvature: Slow aircraft?

At some point I was considering the rear window of the Consolidated Catalina but it doesn't quite seem to fit the bill.

Tony Hisgett on Wikicommons/Source

The hole you show in the other post tells me it is not a gun turret. The hole has a small diameter and looks like a series of screw holes around the edge. This could be a sensor or access panel fitment point. The dome itself could be a housing for a strike/ recon camera. It might have fitted to a self contained pod that fitted to an aircraft or be part of a recon aircraft fairing. There is not much to go on and with no access to service parts records you are going to be hard pushed to identify it for sure, hell... it could even be an old truck part.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Where can find Service Ceiling of an aircraft?
I would like to figure out the service ceiling for Cessna 172N and I couldn't find it anywhere in the POH.
Where can I find it? In POH or somewhere else? If in POH, please post a snapshot of it.

You should use the answer to this question as reference only. The specific ceiling of your aircraft may differ due to configuration or other limitations/alterations and you should use the POH/Reference Cards/Airworthy Certificate for your specific 172 for the most accurate answer.

How do you find the service ceiling? Start climbing and then just keep climbing until it stops climbing....

It is in the Pilots Operating Handbook allright.

As @Dave pointed out, this value can change depending on configuration and other limitation/alterations.

It is in the pilot handbook, before the title page [PDF], under "performance-specifications"


text:
Can someone actually "fly under the radar"?
It is quite a common phrase, usually without having anything to do with radar or aviation. But. Is there such a thing as 'flying under the radar'? If so, why is this (and how low is that)?

I was expecting somebody to have mentioned Mathias Rust by now...

Rust was picked up by Soviet air defenses, but they chose not to shoot him down. His stunt was soon after the KAL 007 shootdown, and Moscow was not willing to get in hot water so soon again, especially if this was simply a lost pilot.

Yes. That's why some airplanes have terrain following radar.

The same way you can fly in the shadow of the Sun early in the morning. That's why airborne radars exist, they are like the Sun at noon. Note that you cannot fly under the radar if the radar is just above you... and the phrase is more accurately: to fly below the radar horizon.

@PhilPerry the decision not to engage Rust was not made in Moscow, but by local commanders afraid to face the same reprisals as had hit those responsible for the KAL007 shootdown. They ended up facing reprisals anyway of course, this time for NOT shooting down the intruder.

I've read that navies do what it's called "sea skimming" to achieve this. Jets or missiles will fly at low altitude above the sea surface as it approaches its target to avoid radar or ir detection. I'm still not sure if the Navy put this technique as a standard, though...

I wonder whether this phrase entered the popular lexicon because of Dr. Strangelove, where a B-52 "successfully" avoids Russian radar by flying at low altitude.  This might have been possible given 1964 technology, even if it's not possible today.

In many cases, yes you can fly under the radar because typical civilian radar is line of sight, meaning that it has to have a straight unobstructed path to an object in order to "see" it.
This is because it works by sending a radar signal out and waiting for it to reflect off of something.  If it reflects off of another object, like the ground, a mountain, a building, a thunderstorm, etc. then it won't see what is behind it.
Since the earth is round, flying "under" the radar is flying beneath the coverage area that the radar can "see" directly from where it is, and the height of radar coverage depends on the distance from the site as well as the terrain.
An example is here:

The top half shows how the curvature of the earth affects it and the bottom half shows how other objects can shadow radar (even though is is using aircraft radar, the same principle applies).

That being said, there are other types of radar and other ways of utilizing radar that minimize this problem and make it nearly impossible to fly under it.
One common type in use is the Tethered Aerostat Radar System:

This is downward looking radar attached to a 25,000 ft. tether.  From 15,000 ft. it can detect aircraft and even vessels all of the way down to the surface of the ocean out to 200 miles.
Another type is Over-The-Horizon Radar which can see further by reflecting radar off of the ionisphere like this:

Note that doing so maybe be difficult for commercial and military planes, but helicopters(choppers) can do this very easily due to there small size and ability to fly at very low heights like 10 ft.

Private airplanes routinely drop off radar during approaches and sometimes even enroute.  I've been told by ATC that radar contact was lost during an emergency approach to an airport once and another time while enroute over the Northern part of Michigan's lower peninsula.

sweet graphics. thank you for that simple explanation

One should note, though, that flying too low in certain atmospheric conditions will make radar detection easier (because of surface ducting).

It is certainly possible to fly "under the radar." Military pilots practice a type of flying called nap-of-the-earth for exactly this purpose. This tactic is primarily used by smaller fighters and attack aircraft, but larger planes like the B-1 are also capable of this. Here is why this tactic may be useful:
In civil aviation, mountains or other terrain can block radar signals. Going too low in a mountainous area will take you out of their radar coverage. For this reason, controllers have Minimum Vectoring Altitudes. These are based both on the radar coverage and terrain so that ATC can ensure aircraft will be at a safe altitude.
Here is a cross section of how radar coverage may look. Obstructions can block lower portions of the coverage as it radiates outward from the radar facility. The red indicates the normal radar used by ATC (the green is called "over the horizon" radar, generally used for military early warning radar).

Even military radars have a limit of the lowest altitude at which they can track aircraft. This is because the radar signal will also reflect off of the ground and objects on the ground, causing interference. This is called clutter and can be avoided by Doppler radars that detect velocity. The concept of the radar horizon determines the point at which clutter will no longer affect the radar.
The SA-6 air defense system can engage targets using radar down to 100m, and the SA-8 can engage down to 10m. These are both short range systems, though (less than 30km).
This report has some references about areas on ATC radar that are difficult to cover because of obstacles such as wind farms. Because the radar doesn't distinguish altitude, controllers may not be able to distinguish an aircraft within these areas of interference.

Excellent answer!  +1!  Actually, the B-1 was specifically DESIGNED to fly nap-of-the-earth because it eventually became clear that bombers were never going to be able to fly higher and faster than air defenses, so the only way to avoid them was to avoid being seen by them before it is too late.  That of course is the idea behind more modern stealth aircraft as well

Great answer overall, but one minor error.  Doppler radars were actually originally built to overcome ground clutter.  The velocity information provided by the doppler portion of the radar is used to discriminate between moving targets (aircraft) and the ground.  This is why a lot of early airborne Doppler radars emphasized their "look-down" capability.  They were able to see enemy aircraft against the ground by filtering on velocity.

Secondary Surveillance Radars work on 1030 MHz and 1090 MHz. Most primary radars work at higher frequencies. Signals at these frequencies do not follow the curvature of the earth very well. They work best in line of sight. Aircraft far away from the radar must be at high altitude to be above the horizon, otherwise they are "under the radar"
In flat terrain at 1 000ft, the horizon is about 33 nautical mile away. Aircraft further away will be shielded below the horizon. For 40 000ft, the horizon is about 220 nautical mile away.

L-Band signal horizon
Due to a slight refraction of the signal the practical range is somewhat further than the visual line of sight.
Keep in mind that the signal is also blocked by terrain; nearby hills and mountains obstruct views.

@RalphJ Just noticed you changing my radar answer. It's fine when you add a comma for clarity (although confusing for me since in my country we use the comma as a decimal separator), but please be careful not to change the magnitude of the number (you increased 1000ft to 10,000ft).

Sorry - I thought I was reading it as 10 000 feet the first time thru. Thus the value of separators!

@RalphJ You clearly have a point there, or should I say comma? :-)

To your question of "how low": In the US, radar coverage is generally pretty good, but there is a distinct floor below which an aircraft cannot be picked up by a radar system. The figure below shows this radar floor in the US:

The figure was taken from here, page 73.
With the introduction of ADS-B as a surveillance source, this will change quickly. Areas where radar coverage is poor can be improved by the installation of an ADS-B receiver, which is significantly cheaper than a radar installation (~25X cheaper).

Any idea what the white parts are in Nevada and California ?

My guess is that its Area 51 in Nevada and Edwards Air Force Base in CA.

@Criggie most of the white patches do not mean that there is no radar coverage, they mean that there are no (or very few) flights there. Notice the title "lowest radar track". For each point they plot the lowest track they got. Where there were no flights, there are also no tracks.

@nodapic I think you are on to something, but slightly off in the reason. The area in California looks like the China Lake restricted area and Death Valley. Area 51 is only a small part of several restricted areas north of Las Vegas. Also note that the white area is 2,500' and I know there is no low-level radar coverage around Death Valley.

@JScarry Good catch; those shapes to align better. The white area is is in excess of 25kft though; that scale is 10^4 (had to check the original file and text, figure above isn't the best)

It also depends on the premise of the radar system. The civilian ATC radar system is based on the targets being cooperative (transponders) and they actually want certain aircraft to be invisible:  private aircraft not using controlled airports, for example. The system also deliberately removes slow-moving targets like flocks of birds.
Military radars, of course, assume the opposite. They deal with the line-of-sight problem with remote installations (e.g. DEW line), over-the-horizon systems that can boil water at short ranges, and during a battle will put the radar station overhead (AWACS). Mounting your radar antenna at 30,000 feet will extend its range a long way, and make it both harder to blow up and easier to replace.

"they actually want certain aircraft to be invisible: private aircraft not using controlled airports, for example" - Who are 'they'? This isn't true in the U.S. where private aircraft pilots are encouraged to use a transponder and talk to ATC, even if flying in airspace where not required by the FARs.

A large number of GA aircraft don't have transponders. I don't think it's true that civilian radar utilises almost exclusively secondary radar. They have to use primary radar to see all the traffic. Secondary is then a bonus and relies on cooperation, as you say.

ATC radar is line of sight and doesn't follow the curvature of the earth. It does a bit but not enough to stay parallel to the ground.
The radar is also blocked by terrain (read: mountains).
This is one of the limiting factors of radar.

First, yes, it is entirely possible to fly under the coverage area of most civil radar systems. Other have already explained that in detail.
However, there are radar systems that are not so limited by line of sight, and are able to see Over the Horizon using various techniques. So just because you're out of or below the range of the far-away radar does not mean that no one is watching you.

Yes, staying at low altitudes can mask your presence to ATC primary radar systems as well as all but the most advanced military radar systems.  Low azimuth scanning by a radar antenna introduced unwanted electromagnetic interference with its signals also known as ground clutter.  It becomes much more difficult for a radar set to detect a single target flying in this clutter until the aircraft is much closer to the transmitter, thereby greatly reducing the detection range.
Military pilots in non stealth combat aircraft will often opt to fly at low altitudes to hide in clutter.  While this does offer a measure of protection against command guided surface to air missiles as well as fighters, it makes the aircraft vulnerable to short range surface threats like close in radar guided AAA or MANPADS.
Drug smugglers perfected an art of low flying to avoiding detection in the late 1970s and early 1980s by flying mule aircraft low on the deck over the ocean.  See Mickey Munday's or Barry Seal's story from the documentary Cocaine Cowboys where they talk about flying an aircraft into the Bahamas at night 50 feet above the ocean.  They claimed that as long as they couldn't see the glow of lights from Tampa, FL, they were too low to be detected by ATC.

In addition to the other answers, radars need to account for moving objects on the ground. To deal with this, most radars don't want to pick up a moving truck or a tree swayed by the wind at all.
There's just too much stuff moving on the ground already, so even if the radar waves do reach you, if you're low enough you're part of the noise at ground level.

Is there such a thing as 'flying under the radar'?

As already well explained, it is possible to hide in the shadow of obstacles when the radar is on the ground. But if the radar antenna is high enough and the angle of view is greater than the slope of the obstacle envelope, hiding is unpractical:

The extend of the radar shadow depends on the radar height
Radars can be located on high points, or can be airborne like AWACS. Airborne radars are not required to directly overfly the targeted area (not desirable for side-looking radars using the Doppler shift to detect moving objects). Moreover with an airborne radar:

Remaining in the shadow during a significant time would require matching the terrain configuration and the trajectory, which may not be tactically useful.
If such match is possible, it is possible to have a second airborne radar to illuminate the shadow side of the obstacles.

Boeing E-3 Sentry with its characteristic shape is a well known aircraft, there are other airborne surveillance radars with fixed or rotating aerials, manned or UAV.

NATO E-3A over Italy, source NATO

E-3A, source
E-3 operational range is about 400-500 km. From NATO:

An E-3A can detect low flying targets within 400 km or 215 nautical
  miles; and at medium altitude targets within 520 km or 280 nautical
  miles.

and

One E-3A flying at 30,000 ft / 9,150 m has over 312,000 km² in its
  field of view. Three E-3As in overlapping orbits can provide complete
  coverage of Central Europe.

E-3 embed a synthetic aperture radar (using the distance traveled by the radar during the pulse roundtrip). The principle is to detect moving targets against the stationary background using Doppler spatial filtering (see theory here).
E-3 can stay in flight for about 10 hours without refueling, and are all able to be refueled in flight.

E-3 Sentry refueling from a A310 MRTT. Source Chosun.com
Indeed airborne radar must flown to the area of interest and then must remain in place for possibly a long time. This is a costly operation reserved to military conflicts and similar situations.
These months a couple of NATO E-3 are orbiting over Northern Poland to monitor activities in Western Ukraine. As the related aircraft broadcast ADS-B messages, it's easy to look at their activities on tracking sites:

Two NATO AWACS orbiting over Poland, source Plane Finder
Two E-3A orbit near the sea (top) and the refueling area is about 400 km South-East (bottom). A KC-135 tanker is flying racetracks while waiting for aircraft to refuel and a larger pattern while delivering fuel.
Detecting low flying targets is only one of the many uses of the E-3 Sentry, which roles also encompass electronic signal intelligence and operations command center.

Could you elaborate on "positioning a radar satellite over the location"? AFAIK military radar sats are all low-orbit or SSO, so you can't position them over a location, at best you can overfly it once a day, at a time and trajectory exactly known to your opponent in advance.

Also, AFAIK, ground shadow is definitely not THE reason for using AWACS. The reason for using AWACS is because, when fighting over enemy territory, it's going to be your only radar in the area. It will also stay a good hundred miles away from the action, so as not to fall ingloriously, so it's the left picture, not the right one.

@Therac: Relocation: You're right, I forgot there is no radar sats at GEO altitude; AWACS: Agreed and fixed.

Especially historically, before radars were connected to computers, a radar whose beam reached low enough to bounce off tall objects on the ground would for many purposes be less useful than one which was adjusted to only see objects that were airborne.

Retired F-111 A-G and EF models, and existing B-1B Lancer aircraft use(d) Terrain Following Radar (TFR) to fly under radar coverage.

authors: Vladimir F Героям слава


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Why must IFR be cancelled?
Watching flying videos and listening to LiveATC, you will sometimes hear a pilot cancel IFR approach.
Why does the ATC care if you are on IFR or VFR? So long as you get on the ground safely, it seems like it wouldn't matter if you were looking at instruments or out the window.
Surely the "radar service" is still running for other aircraft, so it seems it's merely a formality to indicate how a craft was navigating in the event there's an accident. Is there another reason I'm not thinking about?

Are you sure they canceled IFR with the tower and not approach? It's common to cancel IFR when you're visual with the field, and it's a non-towered airport. That way you don't have to call them later to do so (no cancellation means they have to trigger SAR, at a towered airport the tower will do it without asking when you land), and you might not have radio coverage so you'll have to do it on the phone.

@falstro That could just be my error. I'm not a pilot, so very new to terms and such. It likely was Approach they cancelled with. I"ll update my question.

It's all about making sure everybody knows what's going on. While you are on an instrument approach and thus flying IFR, ATC is responsible for spacing you, giving instructions on heading and speed in order to fit you in with other inbound aircraft. In that situation they expect you to confirm and follow those instructions, and if you don't it makes for a lot of headaches.
If you're on a visual approach, such as when you've cancelled your IFR flight plan after descending below sparse clouds with the runway now in plain sight, then the tower knows not to give you spacing instructions; they instead space IFR traffic around you, while other VFR traffic just has to maintain their separation minima from you. Knowing that you're on a visual approach means ATC won't waste their breath trying to get you to adjust your airspeed, altitude or course to follow a traffic pattern; they'll just give those instructions to other aircraft in the pattern to maintain a steady traffic flow.
... unless you're in Class B space. If you are flying into a Bravo airport, you can still request a visual approach, but approach control has to OK that change (especially for airliners), and ATC is still required to provide separation services to you whether you're VFR or IFR, so they can still give you instructions regarding your airspeed to make sure you fit into the IFR traffic pattern. This may, at times, require an uncomfortably fast landing for GA pilots being spaced in between commercial airliners at a busy time. Some Class Bs like Phoenix or DFW will have a runway more or less reserved for smaller aircraft so there's less disturbance to commercial airliners with higher approach speeds, but not all airports have that luxury; if you want to land your small single at O'Hare or Dulles, you'll probably find yourself spaced in-between airliners and forced to very precisely time your approach so you can touch down and clear the runway in time for the plane behind you to take off. If traffic is heavy, you may not get in if you greet them with "Hello O'Hare Approach, Piper 354 Alpha...". As soon as the O'Hare controllers hear your GA small-prop callsign, if the pattern's too busy they'll deny you Bravo entry and recommend you head for a smaller airport like Chicago Exec or Gary.

Both answers are very informative, however I think this answer is a little more complete in regards to the "why" component of the question.

There's really no "must" for in-flight cancellation - If you want to you can continue under IFR all the way to the ground, even if you've broken out and are in VMC, and then close your IFR flight plan once you're on the ground (by radio if still in contact with ATC, or by telephone).
(You must however cancel your IFR flight plan at some point or ATC will assume you have made a smoking hole in the vicinity of the runway and send people looking for you.)
Pilots may cancel IFR in-flight if they've broken out of the clouds and are operating in VMC (with all appropriate visibility and cloud clearance requirements met, and the weather such that the pilot can continue to meet them until they land).
The big advantage of cancelling in-flight is that it helps out ATC.
When operating IFR at a non-towered field operations are handled on a one-plane-at-a-time basis: If you are on approach under IFR ATC can't take another IFR aircraft - inbound our outbound - until the last one they authorized departs the area or calls in to cancel IFR.  If that aircraft cancels "early" (in flight, because they found VMC under the clouds) they can bring another IFR aircraft onto the approach, which avoids having to stack them up in holds or other traffic management tricks.

So, it seems cancelling IFR is really just to help out other pilots and ATC? Can one land a plane by looking out the window (VFR) but still be under IFR plan?

@SnakeDoc With the exception of aircraft that are capable of autoland all landings are made by looking out the window: Even if you're in IMC you need to see at least some portion of the runway environment in order to land on it. For that matter even with autoland the pilots are still looking for the runway and monitoring the landing to abort if they don't see a runway under them by a certain height - the exception being Category IIIc approaches, which would allow zero-visibility landings.

@voretaq7 - all very correct, and I would just add that no Cat IIIc ILS approaches exist yet; the spec exists, but the best GPS-based approaches can still have a margin of error of about 10 feet in any dimension, which at "transition" is the difference between a greased landing and the airline having to pull the plane to replace its gear and tires.

@KeithS I think the issue is more of what you do when you are on the ground. Airplanes don't use GPS for height measurements (it can't, GPS gives ellipsoid height, not AGL so radio altimeters are used). Since there is no guidance system for the ground once you hit zero-zero and the aircraft stops on the runway, you can't taxi in.

@RonBeyer - very good point. That also means that to perform a Class IIIc ILS approach, the aircraft has to have a radar altimeter, and thus it's more about the aircraft's equipment than the facility's at that point.

IFR flight requires separation minima to be applied by ATC.  When an aircraft reverts to VFR (cancels IFR), the pilot takes on the responsibility for separation from other traffic.  By cancelling IFR, you relieve ATC of the restrictions incumbent with instrument traffic requirements.

I've never heard of a requirement to cancel IFR per se.  That's left to the PIC's discretion.  I do know that if you are flying an instrument approach into an untowered airport, controlled airspace around the airport ends at 700' AGL i.e. the transition between Class E Airspace and Class G Airspace at which point ARTCC can no longer provide control and radar services in this airspace.  The flight plan does continue to operate under instrument flight rules as required, particularly if you have to go missed as you will immediately switch from the CTAF back to center or approach and declare missed.  This is not a problem with a towered airport as you will be immediately handed over from ARTCC or approach control to the tower for the rest of the approach and landing.  As mentioned above this can help alleviate workload for approach controllers as well.
Sometimes pilots will cancel an IFR flight plan when arriving at an airport if the local weather accommodates VFR flying for reasons of expediency;  you can quickly enter the VFR traffic pattern and land as opposed to being vectored out to an initial approach fix for flying an instrument approach.


text:
Why is the treatment of magnetic variation different for NDB and VOR?
Why in solving numerals of NDB and VOR, do we apply variation at the station in case of VOR and at the aircraft in case of NDB?

I removed your second question because we only allow one question per post. Feel free to ask that one in a separate post.

The reason is, that for a VOR, the receiver in the aircraft determines the radial based on calculating the phase shift and as the VOR is oriented to the magnetic north of its location, we need the variation of the station.
Think of it as a lighthouse which changes the color through a full turn and hence you can just tell by the color, which radial you are on.
For the NDB however, the ADF receiver uses a sense/loop antenna to determine a direction and the needle is overlaid onto a course card which is oriented to the magnetic north of the aircraft.
Think of it as a pilot looking out of the window to see a lighthouse that has a white omnidirectional light.
So as you can see the angle is once determined at the VOR and once from the aircraft and hence the different variations apply. Nevertheless I think this was espacially emphasized for examination, as it is not that important in practical flying nowadays.

For VOR it is not just variation of the station, but variation of the station at some past point in time when it was last aligned. Because magnetic variation changes over time, but the stations tend not to be realigned often, or ever at all, because then all the charts would have to be updated and that could be additional source of errors.

@Jan_Hudec what's your take on variation in aircraft for ndb

@SourabhJain you use whatever variation is depicted on the chart for the aircraft's position.They use a World Magnetic Model of the earth's field, that is computed and revised every 5 years, the "5 year epoch", by a joint US and UK defense geospatial project.  The chart will include the date of the epoch model in use. The current one is 2020, and a new one will be issued for 2025.  So if you have a chart published in 2019, the variation lines will be from 2015, but if you have a post 2020 issue chart, its variation data will be accurate. In any case, a degree or two of error is not a big deal.


text:
Why does GBAS broadcast Final Approach Segment data when SBAS does not?
Ground Based Augmentation Systems broadcast message four, the Final Approach Segment, along with corrections for GNS signals in messages one and two. Since the FAS is essentially a semi-static approach plate, it seems like it could be distributed by subscription along with all the other info in a flight database instead of wasting VHF link bandwidth as it does. In fact, the Satellite Based Augmentation System uses the flight database subscription method.

For SBAS, the FAS data block is stored in the aircraft’s navigation database, while for GBAS the FAS data block is broadcast as a VHF data message.

What was the purpose for the GBAS design choice? It is impossible for the SBAS system to do this, but once the less constrained method was established, it seems like both systems should use it.

The reasons GBAS and SBAS are the way they are goes back to decisions made in the early 1990's when the concepts were first proposed. When the push started for satnav approaches it was obvious that augmentation was necessary to meet the accuracy and integrity needed for approach procedures. The FAA tasked RTCA to develop the standards and that was delegated to Special Committee 159 (SC-159).
SC-159 is a very large committee with representatives from government agencies, airlines, aircraft manufacturers, general aviation, avionics suppliers, and pretty much anyone with an interest in the system. Because of the huge amount of work and the differing systems the work was broken out to separate subcommittees. So while there were some people working on both subcommittees, the subcommittees each took there own path.
GBAS was being promoted by the FAA to be a functional replacement to ILS with support for CAT I and eventually CAT II/III operations. This needed support of the airlines who were only willing to go along if it didn't add significantly to their costs (preferably it would provide capability where ILS wasn't feasible and give them additionally capability at little to no cost.) So a fundamental goal of GLS was to be as operationally similar to ILS as it could get - minimal crew training, minimal aircraft system changes.
That last bit is key as the ILS is a DAL A system tied to the autoland system which is very expensive to certify. The avionics solution to this is the multi-mode receiver (MMR), ref: ARINC 755. The MMR allowed for retrofit as it occupied the same package as the legacy ILS receivers.
The MMR added a GPS sensor (which wasn't standard in the early 90's) and it allowed for integration with the ILS and its interfaces. The first MMRs were just and ILS and GPS sharing a box. But later versions added a precision approach navigator (PAN). The PAN could use the ILS output busses to provide the "ILS Look-Alike" output. But the GPS needs the augmentation data. This is broadcast from the GLS ground station on a VOR/ILS frequency. So the ILS receiver (a software defined radio) is repurposed in GLS mode to receive and decode the VHF data broadcast (VDB) from the ground station. It can then provide the augmentation data to the GPS and the FAS data to the PAN.
The reason for the FAS data being broadcast and not being in the nav database is that database is located in the FMS, not the MMR and the FMS is not a DAL A system. It also follows the concept that the ILS/GLS is a stand-alone unit that can support a precision approach even if other systems have failed.
Conversely, SBAS was pretty much ignored by the airlines (they only added WAAS GPS receivers when ADS-B drove the need.) SBAS was championed by the general aviation community that want RNAV approaches into airports that didn't have good approach options - no ILS, maybe a VOR or NDB approach. An RNAV approach was a big step up. Due to the large number of small airports that desired the capability, SBAS was more cost-effective than a GBAS approach. It was also cheaper for the user as it was contained within the GPS navigator/FMS. The limited bandwidth of SBAS forces the procedure data to be included in the nav database. But SBAS will likely never go beyond LPV capability which is acceptable to the GA community.
So the different needs of the GBAS and SBAS resulted in the different solutions.

Great insight Gerry. About WAAS and ADS-B: ADS-B doesn't need WAAS. It's the FAA that requires WAAS for an ADS-B installation, but most other countries don't require any SBAS for ADS-B. From the safety and performance analysis of the ADS-B applications it is very hard to derive a need for WAAS. It may have been added to the ADS-B mandate to justify the development of WAAS

@DeltaLima The comment about ADS-B and WAAS was a bit of a simplification as there are other factors as well. One was supply side. The Airbus RFP for an MMR for the A350 (c. 2007) wanted GLS support and DAL A, and it had to comply with EASA's latest guidance for DAL A. That included dissimilarity, which the then current unit didn't meet. So a new (expensive development) chipset was needed, and including WAAS meant the chipset could be sold into the bizjet market where WAAS  is desired in addition to the airlines. I also worked SC-186 (ADS-B) back then. Getting consensus there was a challenge.

I was in SC-186 too (actually Eurocae WG 51, but the majority of our meetings were joined), but I only joined the meetings just after DO260B went through FRAC (I first joined in 2010 in Chicage IIRC, DO-260B FRAC meeting was end of 2009). I can agree that getting consensus was challenge :-)

The GBAS method allows for more dynamic implementations than the database method. Databases are updated only on the AIRAC cycle date, and getting a change through requires months of preparation beforehand. The GBAS message can theoretically be changed overnight.
For example, if an airport needs to urgently displace a runway threshold (e.g. because of unplanned maintenance or an incident) this can be done overnight with GBAS.
If a database change would be required, this can't be done on short notice. In the AIRAC system the AIS organisation has to publish the data 42 days in advance to allow users or their suppliers to prepare and distribute the updated database.   Getting a displaced threshold through would take at leas 42 days, and at most 70 days. The same for moving the threshold back. For airports it is a huge benefit to have that flexibility.
For SBAS it is impossible to provide approach data, since the same SBAS signal serves a very large airspace with countless airports in it. For example, the US WAAS system uses 3 satellites at the moment. Providing approach data for all USA airports would result in very inefficient use of bandwith: approach data for all of the US would be broadcast to every location in the US. That would either require very high throughput (bandwidth) or result in very low repetition rates (making it less practical if you have to hold for several hours to obtain the approach data).

I don't think the GBAS (GLS) approach data would change out of cycle.  I do think it is a good idea as it does not require a current database to fly the approach.  The data will be current on the VHF frequency.  The pilots will need to have current approach plates though.  I don't know if the transitions or intermediate segments are broadcast so those may require a current database.

@wbeard. At the moment a current database is required. The problem we have is that the current AIRAC system is very rigid, but it's almost impossible to move away from it. GBAS offers a first stepin the roght direction, but by itself it will not enable more flexibility. But combine it, for example, with an autonomous aircraft and the possibilities are clear.

"The GBAS message can theoretically be changed overnight". This is a mis-characterization of how navigation data is managed. The FAA has the same approval rules and process regardless of distribution method. The average delay between SBAS and GBAS update methods is half the 28 day AIRAC cycle, or 14 days. What message four data is so crucial or changes so frequently that 14 days makes a difference?

It's way more than 14 days, and also more than 28 days to go through the process of an avionics database change. 42 days before the change takes effect, the AIS organisation has to publish the data to allow users or their suppliers to prepare and distribute the updated database. So if you urgently need to displace a runway threshold (e.g. because of unplanned maintenance or an incident) this can be done overnight with GBAS. If a database change would have been required, it would take at leas 42 days, at most 70 days. For airports it is a huge benefit to have that flexibility.


text:
How does the ADS-B signal transmission randomization work?
As the FAA mentions, the ADS-B messages like Identification, Position and Velocity are transmitted randomly uniquely between $ 04 \pm 02 $ sec.
How does the transmitter define that randomization? Is it standard or fixed or else who decides that?

Presumably it uses a form of a Random Number Generator, like any other computer would use to generate random numbers. I'm also not sure that "standard/fixed randomization" is a concept that exists.

The random delay is introduced by a function called General Formatter / Manager, it is uniform and its unit of time must be less than 15 ms. Non cryptographic uniform random sequences are usually obtained using Linear-feedback shift registers but I don't know what is used for ADS-B Out..

The standard DO-260B dictates that ADS-B devices must generate uniformly distributed random numbers. They do that by using a PNRG algorithm.
Note sure where the number $ 04 \pm 02 $ comes from, indeed the broadcast randomization specifications are the following (source§7.3.2):

Message
Condition
Interval

Airborne position
-
$ 0.5 \pm 0.1 $ sec

Airborne velocity
-
$ 0.5 \pm 0.1 $ sec

Surface position
Moving
$ 0.5 \pm 0.1 $ sec

Surface position
Stationary on ground
$ 5 \pm 0.2 $ sec

Aircraft idententification
Moving or Airbone
$ 5 \pm 0.2 $ sec

Aircraft idententification
Stationary on ground
$ 10 \pm 0.2 $ sec

TSS
Airbone and valid state
$ 1.25 \pm 0.05 $ sec

Aircraft Operational Status
Various conditions
Complex (see source)


text:
How do anhedral and dihedral affect the efficiency of a wing?
Higher pressure air on the underside of a wing generally rolls outboard around the wingtip and over the top of the wing reducing lift and therefore increasing induced drag.
My intuition would tell me a wing with a dihedral would increase this effect as the higher pressure airflow on the bottom of the wing would flow outboard easier than anhedral. Is the opposite true with anhedral? Would the airflow flow inboard?
Are there any other factors that could contribute to efficiency?

The lateral flow effect you are talking about affects both top and bottom so would roughly cancel out. Pressure gradient induced lateral flow is outbound on bottom but inbound on top. The wing is at a fairly low angle of attack in cruise flight; even near stall AoA is only about 18-20 degrees and retains fairly normal flow up to that point.
With very large dihedral or anhedral the isolated airfoil section would produce lift just as efficiently as a flat wing but the overall aircraft is less efficient because it wastes the lift produced. At 45 degrees from level the wing would need to produce lift equal to 1.4 times the aircraft weight. Same as being in a 45 degree bank but with no turn as the wing vector forces are fighting each other. At low angles the wasted lift is not significant compared to the effect on handling and stability. At 5degrees dihedral or anhedral the lift is 1.0038 times the gross weight, or 0.38% less efficient.


text:
How does altitude affect the TAS and thrust of an electric fan powered aircraft?
I'm confused about the relation between IAS, TAS, thrust, and shaft power, for an electric application. Yes, higher air is thinner, and thrust goes down due to higher airspeed. What I've researched uses only air breathing engines for calculations.
Gas turbines either are limited to lower altitudes or higher altitudes with high speed, to intake enough air to maintain combustion. The other limiting factor is they have very strict maximum rpm. Modern turbofans do not have a variable transmission to counteract this. The same concept applies to electric motors, to a lesser degree.
For example, an electric driven ducted fan has a tip speed of Mach 0.85 and was set to maintain the same power output of say 50kw no matter the altitude.

What would happen to the TAS, IAS, thrust and the shaft rpm of the motor as well as tip speed of the ducted fan as the altitude increases?

Is the power necessary for an increase in TAS and a constant IAS the same up to the point where the increase in rpm (less load) due to thinner air causes the fan blades to see supersonic tip speeds?

If an aircraft can fly at 60 knots with 50 kw at sea level, does that mean at 50,000 ft it can realistically fly at 185 knots TAS for the same given power? (I used this calculator).

Also, how does thinner air affect static thrust?  Is the same thrust maintained as long as the same amount of power is given to spin the fan?

The Helios was an electric powered prop driven aircraft that achieved an altitude of over 96,000 feet and maintained it in level flight for more than 40 minutes.

as altitude increases

You maintain wing lift with constant IAS until the wing airflow approaches the speed of sound (TAS increases).  Shaft power output must increase to spin prop faster to maintain thrust or... changing prop pitch is helpful instead of increasing rpm.  This helps avoid the "sound barrier" for the prop.

as motor rpm increases

Even when not limited by supersonic prop tips, increased engine bearing friction from higher rpm requires a greater power draw.  Again, the ability to vary prop pitch is enormously helpful to maintain optimal prop AOA as TAS increases.

can I fly with the same amount of power at 50,000 feet as I can at sea level

You can get a lot closer by designing your aircraft to fly at 50,000 feet by:
 1.  Reducing wing loading by removing weight
 2.  Increasing wing aspect ratio and/or increasing wing area
 3.  Increasing the **area** of your prop so you can push more air at the same rpm.

With props, you must compensate for thinner air, but higher rpm is not the only way.

"You maintain wing lift with constant IAS until the wing airflow approaches the speed of sound (TAS increases)" - and, if you design your wing right, you can maintain wing lift with constant IAS right through the speed of sound and out the other side!

First let's look at the difference between IAS and TAS
TAS is your true airspeed and is independent of altitude, it's the speed at which you're moving through air. If there is no wind it is equal to your airspeed. On the other hand IAS is the airspeed you read on your flight instruments as indicated airspeed and is a function of the dynamic pressure. Your pitot tube is measuring the stagnation pressure and deducing the static pressure you get the dynamic pressure related to the airspeed.
$$ P_{stagn}=P_{static}+\frac{1}{2}\rho V^2$$
As your instruments are calibrated for a given $\rho$ the indicated airspeed IAS will be different than the TAS with variation of the air density. IAS is used to provide a good idea of the aircraft performances as in drag and lift equation the term $\frac{1}{2}\rho V^2$ is always there. At same IAS, the aircraft aerodynamic performances will be the same  whether you are at see level or up a mountain.
Now moving to the engine part of the question. Modern turbofans actually work with fairly constant airflow speed inside fixed by their design. Thrust is produced by accelerating air through the engine. The more air you can accelerate and the more speed increase you can provide the more thrust you get.
As the exhaust leaves the engine nozzle at a fairly fixed velocity, the acceleration provided is directly linked to the incoming airspeed, and here it's the true airspeed that matters. The faster the aircraft speed, the less the intake air is being accelerated. Therefore thrust decreases with increasing airspeed.
Furthermore the higher you fly the less air density you have. Then for the same volume of intake air passing through your engine, less mass is accelerated and therefore thrust is also reduced while flying at high altitude.
Both effects are mitigated by the fact that flying faster increases compression in the intake and lets the whole engine operate at a higher pressure level, thus increasing the output thrust. As airspeed increase, more volume of air is directed in the inlet where it needs to slow down before entering the compressor, thus increasing the inlet pressure your engine is seeing.
Modern turbofans are highly oversized, as for twin engines airliners they must be able to fly level for more than 180min with one engine shut down (ETOPS 180 certification). Therefore they never use the maximal power output they can generate even at take-off. Then even if with the altitude and airspeed thrust decrease there is still plenty enough to cruise at transsonic speed. Finally the shaft power is a function of the torque and RPM of the engine. The torque is directly related to the thrust and the RPM are maintained at quite a constant value in new engines. Therefore if thrust decreases, the aerodynamic torque on the fan decreases and the shaft power required to drive it will decrease. Maintaining the same IAS means your drag will remain constant in level flight whatsoever your flying altitude. And thrust requirement remains constant. On ducted fan the inlet compressive effect at high speed mitigate the need of higher RPM. On propeller on the other hand, if you don't adapt your blade pitch, at constant power output, the RPM will increase which is not really good for the engine and the blade tip going supersonic. If you change your pitch your blade can remain at constant speed and the RPM will remain constant.


text:
Are the press reports of this incident plausible?
On May 21st, before an Air Berlin flight from Düsseldorf to Stuttgart (~340 km, 210 mi), a hole in the fuselage of the plane was discovered by passengers. It is claimed, that the crew continued flight preparations, dismissing warnings and only abandoned the take-off after the pilot was pressured by passengers to take another look. He is said to have deemed the plane suitable for flying and only abandoned the idea when pressured by passengers to check the plane again.
Air Berlin claims, that the pilot interrupted his preflight walk-around check of the plane, to return to the cockpit for some tasks. He later continued it and spotted the hole, leading to the cancellation of the flight. Meaning: Everything would have been fine without any passenger warnings anyways.
English sources:
https://theworldofaviationblog.wordpress.com/2017/05/23/passengers-discover-hole-in-the-side-of-air-mistral-atr-72/
http://true-news.info/passengers-air-berlin-found-a-hole-in-the-fuselage-of-the-aircraft/  (has to be true obviously)
German Sources:
https://www.merkur.de/welt/passagiere-entdecken-vor-air-berlin-flug-loch-im-flugzeug-zr-8347888.html
Aviation Safety Report:
https://aviation-safety.net/wikibase/wiki.php?id=195623
For me this whole story seems fishy: I find it unlikely that the pilot and ground crew would have missed this damage. I also find it very unlikely, that the pilot would ignore a serious threat to the safety of the flight. It's his life on the line as well.
So now I have a few questions about it:

Does the airline's explanation make sense? Does a pilot start his outside checks but sometimes interrupt them to take care of business in the cockpit and then continue later?
Would the hole have been a problem in the first place? Was it maybe, from a technical standpoint, really not a problem and the crew later only bowed to the (uninformed) pressure of the passengers? Flight attendants apparently told the passengers to "get in and trust us".
Is such a hole fixable by that hardcore-airplane duct tape, and are such fixes done shortly before take-off?

AvH does not have anything, while ASN(https://aviation-safety.net/wikibase/wiki.php?id=195623) links to a focus.de article, and it seems to be a user-added entry.

Thank you Federico, yes the story was covered by most german news-outlets.

Np, was only to check the sources that most likely would have independent data. Please consider making the title less loaded (and please also rephrase the "Reality Check about “Hole in Fuselage”-Air-Berlin story" part to have only a question in the title)

Okay, I have also added your link to the question.

I just wanted to connect it to the actual story behind it. I am actually interested in how pre-flight routines can explain the corner-stones of the story, because I don't feel that general-purpose news storys can do that (it's not big enough for them to involve actual pilots etc.). Feel free to adjust the title how you deem more appropriate.

@mins Well, the title of the question was reworded by Pondlife to refer to just the article. Initially I included some cornerstones of the story as actual questions. It seems the consensus about titles is not very deep. ;-) Please also see my previous comment.

It's an interesting question.


text:
What is the difference between "anywhere" and "other than congested areas" in regard to minimum safe altitude?
Just missed a PPL written exam practice test question that asked me what the minimum safe altitude was over areas "other than congested areas". I chose "An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface."
It turns out this is the answer to the question for the area of flight called "Anywhere". The answer for the area of flight called "other than congested", however, is "An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure."
I can now handily regurgitate the correct answers on the written exam for either stated scenario/area. However I'm wanting to know, is the FAA trying to tell me something here? What is the difference between "other than congested" and "anywhere"? Is "other than congested" presumably more congested than "anywhere"? Anything to take away from this hair splitting other than grumbling about the FAA?
FAR 91.119 is as follows:

Except when necessary for takeoff or landing, no person may operate an
  aircraft below the following altitudes: Anywhere. An altitude
  allowing, if a power unit fails, an emergency landing without undue
  hazard to persons or property on the surface. Over congested areas.
  Over any congested area of a city, town, or settlement, or over any
  open air assembly of persons, an altitude of 1,000 feet above the
  highest obstacle within a horizontal radius of 2,000 feet of the
  aircraft. Over other than congested areas. An altitude of 500 feet
  above the surface, except over open water or sparsely populated areas.
  In those cases, the aircraft may not be operated closer than 500 feet
  to any person, vessel, vehicle, or structure.

I was taught that "congested area" was the area on a sectional that is yellow, meaning enough lighting to light it up at night. This definition may be apocryphal however.

@rbp I used to think those were just municipally incorporated areas, but after just now looking at the city limits of Spartanburg, SC (whose county is mostly unzoned and unincorporated but fairly populous) compared to the yellow outlined area on the sectional, the sectional's yellow Spartanburg area takes up more area than the city limits. So maybe there is something to that.

The difference is subtle, but here it is:
anywhere means anywhere: At all times you need to operate at an altitude where, should you lose power, you can put your aircraft on the ground without "undue" hazard to anyone on the ground.
Ignoring all airspace considerations, say you're operating over a city (a congested area), and keeping to the bare minimum requirement for altitude and distance from obstacles. Your engine now fails, and your only "landing" options all involve slamming nose-first into the side of a building. You were not operating "at an altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface".
Since we all want to be able to make safe emergency landings this rule is largely common sense with the force of regulation.
other than congested areas is stuff like farmland or open beaches: you COULD operate much lower and closer to obstacles here and still be within the rules above (you're 300 feet AGL over an open field with a barn 300 feet to your right -- The engine dies, you set it down in the field, and everything is cool), but the FAA (and Farmer Brown in the barn milking Bessie) would prefer you not be that close to the barn in the event of say a flight control malfunction.  Most pilots also wouldn't want to be that close to the barn at that low an altitude (unless engaging in an approved aerobatic demonstration with appropriate waivers) anyway, so it's usually a non-issue.
That leaves congested areas - cities, suburbs, crowded beaches, etc - where the FAA bumps up the minimum obstacle clearances / altitudes for the comfort and safety of folks on the ground.
One could contrive a scenario where you could safely fly at 1500AGL next to a 2000-foot building (like a long, clear, mostly-empty park adjacent to it that you could fly over & use for the "anywhere" emergency landing requirement), but again if something else went wrong you might go into the side of the building. As there are more people in "congested areas" to be freaked out by an airplane flying at a safe-but-rather-close distance, and more people who could be hurt by an unexpected departure from controlled flight, the margins are increased to provide a higher minimum level of safety.
As with Bessie in the barn, most pilots probably don't want to be this close to buildings full of people (and the associate mechanical turbulence), and while circling your friends house in the suburbs is fun it doesn't have to be done low enough to pick out the individual bricks in their driveway and you really should be high enough to land on their street safely if your engine quits, which these minimums will likely allow.

There are really three categories, congested areas, other than congested areas, and under that, the sub-category, open water or sparsely populated areas. I'm not going to get into the nuances of what congested is or is not, but it is worth noting that the FAA considers other than congested areas to include areas that are more heavily populated than merely open water or sparsely populated areas.

@JonathanWalters Yeah, the FAA's definitions are kinda weird - open water or sparsely populated areas is really a subclass of "other than congested areas". I've always interpreted open water/sparsely populated to carve out what I call a Lindbergh exception -- "That one boat in the middle of the blue ocean" or "That one house in the middle of the desert" that you can't get closer than 500 feet from while you're skimming the surface in ground effect so you don't run out of fuel on your distance-record-setting flight.

@voretaq7: How sparsely-populated is "sparsely populated"?

It probably makes sense to state that this regulation will have some variances in different countries.
In the UK, when I sat my pilot exam in 2000, aircraft are only allowed to fly below 500 ft during take off, landing, whilst ridge soaring(gliding aircraft only) and to avoid low cloud.


text:
Has any prior accident been caused by a psychologically unstable and/or suicidal crew member?
I am aware a lot of psychological tests are given to pilots to prevent such a scenario, but those can hardly be perfect, so has any aviation accident been caused (or attempted) by the conscious intention of one of the crew?

I have purged all comments on this question and moved them to a chat room. Further discussion about this question should take place there, or on Meta.

Confirmed (or Highly Probable)

LAM Mozambique Airlines Flight 470: A report from the government of Mozambique states that the captain deliberately crashed an Embraer 190 in Namibia on November 29, 2013. Cockpit voice recorders were the primary evidence in the report, which found that the other crew members were locked out of the cockpit by the captain. There were 33 fatalities, and Mozambique Airlines was banned from flying in EU airspace. No psychological overview was done of the officer.
EgyptAir Flight 990: A Boeing 767 crashed near Nantucket (Massachusetts) on October 31, 1999, killing 217 people. It was found that the first officer, was responsible. The NTSB and the Egyptian Civil Aviation Authority both conducted individual investigations. The Egyptian report states

[the] First Officer . . . passed his full medical examination and psychiatric
  assessment, which was performed by the Egyptian Air Force Medical Council as part of his full medical examination for fitness to be a pilot in the Egyptian Air Force, on December 11, 1958. He passed his medical examination for his Commercial Pilot license on July 27, 1961. A psychiatric assessment was not conducted as part of the medical examination for the relief first officer’s medical review for his Commercial Pilot license. During his military and civilian flying career there was no reported history of psychiatric consultation nor any reports regarding his behavior, either professionally or in groups.
  . . .
  First, there is no evidence to support a conclusion that the First Officer intentionally dove the airplane into 142 the ocean in fact, the evidence available refutes such a theory, a determination confirmed by expert medical opinion, technical and human performance analysis.

The NTSB did not agree that the most probable cause was a mechanical failure. Their conclusions, and the relevant rebuttals by the Egyptian investigators, can also be found here.
SilkAir Flight 185: On December 19, 1997, a 737 operated by SilkAir crashed in Indonesia, killing all 104 people on board. The aircraft was almost entirely obliterated. The Indonesian NTSC report (link broken at the moment) said that the cause was impossible to determine. The pilot appeared to be mentally stable, but there have been some doubts. Cockpit recorders stopped at some time, making the case different from that of, say, JetBlue Airways Flight 191 (see below). The NTSB was not happy, severely criticizing the Indonesian findings. Their analysis seem to rule out mechanical issues.
Royal Air Marco Flight 630: 44 people were killed in a crash in Morocco on August 24, 1994. A government investigation ruled it an intentional suicide
Japan Airlines Flight 350: The crash of a DC-8 on February, 1982, was caused by actions taken by the captain before being restrained by other crew members. Because of their actions, the majority of the people on board survived.
1999 Air Botswana Incident: On October 11, 1999, an Air Botswana pilot deliberately crashed an Aérospatiale ATR-42 into two other planes on the tarmac at Sir Seretse Khama airport, killing only the pilot. He was the only one on board, having taken the plane rogue and then flown it about the airport for hours. All the planes were destroyed, though the other two were unoccupied, as the airport had been effectively shut down. The pilot was on medical suspension.

'Close Calls' but no resultant accidents

JetBlue Airways Flight 191: Midway through the flight, the captain of the aircraft appeared to suffer a nervous breakdown. He began yelling about religion and was eventually subdued by passengers after being locked out of the cockpit by the first officer. He was charged with "interference with a flight crew", according to the FBI, which said

As the plane was leaving JFK and climbing in altitude in its scheduled five-hour flight, [the captain] said something to the first officer (FO) about being evaluated by someone, but the FO did not know what he meant. [The captain] then talked about his church and the need to “focus” and asked the FO to take the controls and work the radios. [The captain] began talking about religion, but, according to the FO, his statements were not coherent.

I also found the same incidences as cpast, from Yahoo! News.

On some of the flights listed, the results of the investigations deemed the pilots obviously mentally unstable. On others, though, the conclusions were disputed, and it may not be possible to truly prove the cases one way or another.

Also, don't forget FedEx 705 http://en.wikipedia.org/wiki/Federal_Express_Flight_705

@slookabill I considered that, but dismissed it, because it was more of a hijacking, and by a non-crew member (at least, not a crew member on that flight).

Why providing the names of the crew members? I doesn't add to the value of the answer, but it may hurt their families who are not responsible.

@mins I have done so.

@mins any damage would have been done already, many of these accidents are several years in the past. The families will have protection against harassment by now.

@ratchetfreak: The question specifically targets persons with mental illness. I don't see the value to disclose and disclose again the names of ill persons, whatever their illness made them do. I'd leave that to a certain press.

I brought it up on meta, if either of you want to weigh in there.

and don't forget the 9/11 terrorists, who suicided by flying those airliners into buildings...

@jwenting As far as I know that wasn't the crew

@HDE226868: FYI, https links to meta.aviation.stackexchange.com cause a certificate validation error (at least for me, on Chrome). Might want to make that just a normal http link.

@Cornstalks Is this better? http://meta.aviation.stackexchange.com/questions/1529/should-names-of-people-potentially-liable-in-accidents-be-withheld

@HDE226868: Yes, thanks!

The most famous example (which probably sparked this question, based on the asking date) -- Germanwings Flight 9525.

@Wingman4l7 Yes, that was the inspiration, it seems. See the revision history.

Regarding SilkAir 185, the majority of the NTSC also agreed that the plane was deliberately crashed, but they were overruled by the NTSC's chairman.

EgyptAir 990
SilkAir 185
JAL 350
LAM Mozambique 470
Royal Air Maroc 630

Those are 5 I found in very little searching. Some of them are disputed (e.g. Egypt's aviation authority maintains EgyptAir was a mechanical issue, the NTSB determined it was intentionally crashed), but these have all been identified by investigators as probable intentional crashes by flight crew. This would be far from the first time this happened. In LAM Mozambique, the copilot was locked out of the cockpit. In EgyptAir 990, the relief first officer did it when the captain stepped out; the captain made it back in but couldn't regain control.
As for attempts, Fedex 705 is a notable attempt by an off-duty second officer deadheading on a Fedex plane to hijack the plane and crash it into Fedex headquarters.

According to an article on  Plane accidents , since 1982, the pilots committing suicide have killed at least 421 people.


text:
Why don't pilots control window shades & seat recliners?
Every time before landing or take off, the cabin crews continuously remind passengers to pull up the window shades, straighten their seats and what not. My question is why can't pilots be given control of these things, at a flick of a button they can open / close all window shades and upright all seats. It's 2015 not 1980.

That shouldn't be the pilots, but the purser who is in charge of the safety of the cabin and of the evacuation.

harass passengers to pull up the window shades, straiten their seats interesting take on actions proven to enhance your chances of survival in the event of an accident.

Um. 1980 wasn't the stone age, you know. There was plenty enough technology in the world to do this back then, too. Which should be telling you that the technology isn't the issue.

@Simon: (Harass)I was just trying to portray a general feeling which I had observed. I would edit it.

@DavidRicherby: the choice of year was was purely arbitrary..

Well, that is on the agenda, but first they are trying to get the passenger ejection capability approved and installed.

As a parent of small children, please no. I don't know where their little fingers are when you push this button.

@TylerDurden Current iterations of that feature only work when slow and unpressurized. They're known as 'doors,' though they can be augmented by features known as 'airport security' or 'cabin crew.'

Because the crew have to check the seat belt is fasten or not, it cost nothing to ask them to upright the seat

Ok, the seat thing is being potrayed as kind of a a horrifying ordeal. Can't it happen in the current scenario. Also, warnings can  be giving  before the seat's are auto adjusted  and the seats  themselves can have design tweaks to prevent small accidents. It is a known risk today, that batteries can cause fire if they slip between seats in first class.

Perhaps it would be more practical to have a central locking mechanism that prevents passengers from reclining their seats, but doesn't actually move the seats.

On the Boeing 787, the mechanical window shades have been replaced with glass panes which can be made more opaque or transparent by applying electric current to them. (source) The passengers can control their own window's opacity through buttons, but the cabin purser can also control them centrally.

I have noticed that too.. Which means, the newer aircrafts have recognised this as a mean to keep in control certain basic functions.

@Firee : note that, in line with Airskick's answer, those blinds are designed to be fail-safe - lose power, and the window becomes transparent.

As a result, the 787 is a horrible plane to fly on! I had blazing sun in my face all the way from London to Guangzhou, and there was nothing I could do about it. I believe the windows were at their lowest setting (not sure though) but it wasn't dark enough. As GdD said, give the passengers control over their own comfort.

@Firee I would take a guess that the basic reason for auto-dimming windows is weight-saving and reduction of parts count by deleting the mechanical shades. Possibly, reducing the cabin cleaning time is a nice bonus as well.

@alephzero I can't imagine that the electronically-controlled windows actually reduce parts count, let alone fabrication complexity. They add wiring, controllers, etc., which are almost certainly heavier and more expensive than plastic shades. The stated reason I've usually heard for it is that it allows passengers to be able to see outside without having sunlight flood the cabin, which makes sense considering the 787 is designed pretty much exclusively for operating long-haul routes where they normally want window shades closed for nearly the entire flight so people can sleep.

The 787 window frames are about the 1/2 the weight of "traditional" window frames, and part of the weight savings comes from removing the frame for the plastic shade. source. I remember seeing a demonstration of the 777 and 787 window frames side by side at the Smithsonian, and I recall that the frames are both thinner and have larger windows.

I love the 787 windows. I hate it when I'm trying to sleep and one passenger opens their window, floods the cabin with light, and wakes everyone up. Likewise, I like to be able to look outside during takeoff and landing. Take control of window shades away from individual passengers!

Adding to @Airsick's answer there's an important psychological component, which is the illusion of control. Passengers in an airplane have very little they have control of, they are told when they can go to the bathroom and when they have to stay in their seat, they are given their meals rather than choosing when to eat, etc. Passengers have the option to control seat position, tray tables, shades, lights, and entertainment systems to suit their comfort. These things are important as they make people feel better about being shut up in an aluminum tube for hours, even if they make no ultimate difference as to what happens.
If you take control of these things away people would feel they are an intrusion into their personal space, and would not like it at all. People like doing things themselves, even if they have no choice ultimately.

Very interesting thought into passenger psychology

Is there any "hard" research, which confirms that the ability to change the seat position and control the blinds actually makes the airplane passengers happier?

@DmitriPisarenko: I realise that this doesn't satisfy stringent scientific requirements, but, purely informally, isn't it completely obvious?

It would also be something else to cause a flight to be cancelled.  If the window blind system failed and the blinds couldn't be operated manually then the aircraft would be grounded.

Only if regulations require that the passengers be able to look through the windows, which I suspect they don't. Planes take off with broken non-essential equipment all the time.

The CAA requires aircraft taking off or landing in the hours of darkness to close the window blinds and to have occupied seats upright, and seat tables stowed away.

@DavidRicherby I suspect if all of the blinds failed closed, that actually would be a regulation violation (or at least an SOP violation, which is in turn a regulation violation.) It's not so much a matter of passengers being able to see, but cabin crew being able to see in the event of an emergency.

@user23614 Whose CAA? There is no such regulation in the U.S., for example, so it's not an ICAO thing. That seems like a weird regulation anyway. I can't imagine how that would possibly improve safety, but rather quite the opposite. I can see having a regulation for the cabin lights being off during a night takeoff or landing in order for people's vision to be adjusted to darkness, but having the window shades open will not affect that when it's dark outside anyway.

@reirab Having cabin lights completely off would not be a nice passenger experience, especially when flying a holding pattern for half an hour. AFAIK the basic reason for avoiding illuminated passenger windows visible from outside the plane is avoiding confusion with other light signals, e.g. masking flashing beacons and red/green navigation lights, mistaking side-on cabin windows for head-on landing lights, etc.

@user23614 Do you mean window blinds are required to be open? I've never been told that I have to close the window blind for landing or take-off. (And, echoing reirab, which CAA?)

The UK CAA they don't care about inflight or daylight, just takeoff, landing at night.  Don't ask me why, I worked for them and no one there that I asked knew, it's just a requirement.  If they defaulted to closed or the flight was sufficiently empty that the seat could be empty then it would be fine.

@user23614 I add my voice to the list of people who are confused by your claim that window blinds are required to be closed. Every single commercial flight that I took (more than half of which was during nighttime) specified that window blinds must be open during takeoff and landing.

@user23614 It has been discussed here beofre. The blinds have to be open so that you see what's outside. For the very same reason, lights are dimmed for these operations (not switched off, just dimmed). They are more dimmed at night, so that the lighting level inside matches to an extent the one outside. In case of an emergency, this makes it easier to realize what happens etc. On all European flights I took it was like this.

On average, I fly commercially about 15 times a year.  About 10 within the UK, the rest somewhere else in the world.  I have NEVER been on a flight where the blinds were required to be closed, always open.  There is nothing in the CAP or ANO requiring this but it is standard procedure for BA, Virgin, FlyBe, Air France, Thompson, American, Emirates etc etc etc.  Since it is an operational procedure, opening the blinds becomes a legal requirement in accordance with the ANO which states that any lawful command of a crew member must be followed.

@user23614 "If they defaulted to closed or the flight was sufficiently empty that the seat could be empty then it would be fine." I don't understand what you're trying to say.


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Why have none of the US /UK/Japanese airlines ordered the Irkut MC-21 yet?
A new airliner was launched on June 8, 2016 by the Russian company Irkut Corporation.

Source: https://www.flightglobal.com/
The airliner looks good on paper:

Empty plane weight is reduced due to composite and prospective alloy materials and lighter new generation onboard systems
Wide cabin (3.81m), MC-21's cabin is wider than the cabin of an
Airbus A320 by 12 cm and a Boeing 737 by 28 cm. As a result, two
passengers can walk through the aisle without blocking each other.
The wide cabin also supports the biggest luggage racks in its class
in order to accomplish the goals of decreasing MC-21's turn-around
time at the airport (important for charter and low-cost carriers),
providing better comfort for passengers, and making the cabin more
suitable for carriers' purposes
Relatively to the current models MC-21’s engines will emit 20% less
СО2 per passenger seat
High cost operational effectiveness, international certification
under AR IAC, EASA, FAA requirements, individual logistic and
maintenance support during all life cycle will make the aircraft
attractive both for Russian and foreign carriers

Source: Wikipedia
Almost all of the orders look like they come from Russian airlines. But why haven't any US/UK/Japanese etc. airlines ordered any planes?

Ever wonder why an airline chooses a single manufacturer or even model for its entire fleet? Its incredibly expensive to change, or have multiple types of aircraft from the standpoint of personnel and maintenance.

Similar: Why don't Russian aircraft sell as much as their European/American counterparts?

A new, unproven airplane was launched yesterday, and you're asking why there aren't orders for it yet?

@abelenky It has nearly 200 orders. The question even mentions them and has a link to them: https://en.wikipedia.org/wiki/Irkut_MC-21#Orders. It's asking why there are no orders from the west/Japan. All aircraft are "unproven" until they're in service, and all receive orders before they're even built.

I'm not against answering this (and the answers we have so far are good), but isn't this the type of question that usually gets closed as too broad or opinion based? Unless we have someone from the purchasing dept of an airline lurking about, it will be hard to really know why.

It shouldn't be closed for those reasons. It's a question about how purchasing and orders work in the airline industry. The fact that people may have all kinds of wild opinions about what these matters - I mention them in my answer below - doesn't mean that what in actual fact happens is not, after all, a matter of facts rather than mere opinion.

The wider cabin isn't a bonus for airlines - they can't use the additional width to add any more seats, 3x3 is the certification limit for a single aisle, and a wider aisle simply means more fuselage weight to be hauled around for little benefit.

@Moo Some benefits are already mentioned in my question with respect to the wider cabin, like more luggage space and short turn-around times at the airport.

@Firee neither of which is an issue today with either the A320 series or the 737 series. The additional weight being carried for the wider fuselage is more of a negative than those are a positive for airlines.

@FreeMan The platform is about collecting answers from experts so if someone from the purchasing department from an airline could answer it, then it seems that this is an excellent question. The questions that ought to be closed are those for which two experts would not agree on what a good answer is.

@Moo But doesn't it say that the empty weight of the plane is reduced due to composites etc. in the first point.

@Firee but it still carries unneeded weight around because the extra space isn't needed operationally.  Its sub-optimal for its type - it may be lighter than its competitors (although I note that Irkut haven't released the OEW for this type yet), but its not light enough to base the decision to switch an entire fleet over for most operators on.

@Moo By that logic, then Airbus A320 also carries unneeded weight, as it is wider then B737?

@Firee nope, because the A320's wideness allows it to carry standardised payload containers in its belly, for both baggage and cargo, while the 737 has to be hand loaded.  Massive benefit there for the A320s additional width (massively reduced belly loading and unloading times as well as fewer ground handlers required), which the MC-21 does not build on (passenger loading and unloading times are extremely rarely a factor in turn around, and its width does not allow it to carry larger standardised containers, so its useless).

Ordering an aircraft is a very complex business, and implicates a number of matters that don't actually (on the surface, anyway) have anything to do with the aircraft itself. Consider this from the point of view of a western European or north American airline.
Broadly political obstacles
These could include:

international trade agreements and disputes (Russia's relations with much of the world are not very friendly at present)
existing suppliers ("Lovely relationship we've enjoyed since the 1970s; it would be a shame if someone carelessly trampled it underfoot and soured it.")
governments and politicians ("Oh really? Well, it certainly has been nice supporting you fearlessly in Parliament/the Ministry/Congress/against my opponents who hate your guts. Bye!")
national expectation ("Traitors!")

History and reputation
Russian (like Chinese) design, technology, engineering and manufacturing have a reputation in the west that works against them. These things take decades, not years, to be overcome by stellar achievements in those fields (consider how long it took "Japanese" to become regarded as a positive rather than a negative adjective when applied to products).
However unfairly, this feeds in to other obstacles:

customers ("Get on a Russian airliner? No way!")
shareholders ("You're proposing to buy a what?!")

Risks
Then, it doesn't make sense to buy one plane to "try it out". Even with a single aircraft of the type, you'd need the same training, certification, engineering support, etc etc as if you had a fleet of them.
So, you'd be looking at a fleet of them, and now you're facing the purchase of a fleet of aircraft that very much represent an unknown quantity. It's a huge, huge risk; no wonder airlines cleave so strongly to the Airbus/Boeing duopoly - maybe it's not entirely to their economic advantage, but they don't expect too many surprises, which is arguably more important.
Some of these risks:

are simply technical ("How good will the product turn out to be in the long run?")
are economic ("Could the trade climate make spare parts and maintenance prohibitively expensive in the future?")
hinge on international relations ("Could our government ban us from working with this supplier in future? Could a meddling Kremlin disadvantage us?").

How could it work? Will it ever work?
Give it a couple of decades.
If airlines in places like India, Indonesia, Brazil, with fewer historical attachments and political obstacles than in the west, find that the aircraft and manufacturer prove to be good for them, bit by bit we may see that influence trickle into western airlines, especially as those non-western airlines and the economies they belong to expand and become more influential themselves.

These reasons are plausible, but how much plausible? Examples supporting them would be helpful.

@mins, Politics, and the Kremlin getting involved are very real and not just "plausible" reasons. Describing Russia's relationship with the West right now as "not friendly" is a slightly massive understatement. There are currently huge trade sanctions against Russia because of their movements in Ukraine and Syria. And the Russian economy is suffering because of it.

Brasil, except for the fact they have their own aerospace manufacturer, Embraer. :)

@ryan: Politics is one point and the most plausible, agreed. For history, reputation and international agreements, I'm not as sure, I notice that ESA is launching Soyuz from Kourou, ISS is relying on Russian design of module Zvezda and the Russian team for its day to day control, on Soyuz for shuttling astronauts and on Progress for cargo (and during a long time only Progress). There is worse as a reputation and "How good will the product turn out to be in the long run?" is a question that could as well be asked for other countries.

@mins, launching Soyuz from Kourou does not carry that much of a risk for either side and ISS relying on Russian support is older political decision from just after the collapse of Soviet Union when US wanted to prevent loss of the knowledge and experience the Soviet space teams had. And the Soyuz does have better safety record than what NASA had and the people in the space business know it. It still does not translate to reputation of other Russian technology.

@JanHudec: "It still does not translate to reputation of other Russian technology". You're right and I'm not saying the contrary, but the answer should illustrate the statement that the reputation in aviation is bad (the same for other statements proposed).

@ryan Russian economy suffers mostly due to internal reasons. Sanctions just add to the problem, but not so critical as it might seem. And summarizing what Daniele said: our government is great at destroying trust...alas.

CityJet has taken delivery of the SuperJet SSJ100s, one of the first carriers in Europe to fly a Russia made aircraft.
The reason that other airlines haven't placed an order is the fact that you need a completely new maintenance facility, crew, workers, parts storage etc, to maintain the aircraft or you need to completely outsource the maintenance. Since there are no other European airlines operating them you need to fly them to Eastern-Europe for maintenance. (From the US is this difficult given the range of the aircraft)
The second item is no problem for low cost carriers that do not do the maintenance themselves. But low cost carriers prefer to fly one type of aircraft (Easyjet, Ryanair) This saves cost on crews and facilities since everything is focused at one type of aircraft (or family). So a new low cost carrier could consider them, but when looking at the history of low cost carriers is that they start with old planes and when successful replace them with newer and cheaper to operate aircraft.
And lastly the unknown trackrecord and new market (for Irkut) does play a role, Airbus for example had quite some difficulties to sell their aircraft on the US market when they first started, some legacy of that is still visible since most of the US airlines fly an all Boeing fleet. Airbus did get their share of the market by giving huge discounts to US airlines ordering aircraft.
So to conclude, the airline industry is a high tech environment which on the other hand can be very conservative and does a lot of risk management when considering the purchase of aircraft.

@Snowman Frontier has only Airbus 319/320/321s, which is essentially three different models of the same plane.

My observations merely as a frequent flyer of United is that the United Express branded Embraer and CRJ aircraft are actually operated by feeder airlines (like Mesa Airlines) so the United fleet diversity is smaller than advertised.

Mainline Alaska Airlines is 100% Boeing 737.

@blaughw: Only until their acquisition of Virgin America is complete.

@Randall: Nonetheless, the "big three legacy carriers", United, Delta and American all operate significant numbers of non-Boeing aircraft in mainline (i.e. not counting "express" carriers).

Ryanair in the UK only uses 737s. There reason is "This streamlined fleet helps us to keep costs down and safety standards up."

@Randall: complementing on what Nate said, United has about 150 Airbus, American has 400, and Delta has 170. In the particular case of AA, around 40% of the fleet is Airbus.

@NateEldredge, the reason these carriers have Airbus in their fleet is that Airbus sold their aircraft fairly cheap to them compared to boeing in order to secure orders and become active on the American market. Lowcost airlines will always use 1 type of aircraft. Thats why these airlines can be a big client for a manufacture since it is very unlikely that they will switch:

http://www.thejakartapost.com/news/2015/08/20/lion-air-welcomes-new-boeing-737-massive-expansion.html
http://centreforaviation.com/news/airasia-orders-200-a320neo-aircraft-powered-by-leap-x-engines-108525

@Brilsmurfffje: Regardless of reasons, you stated "most of the US airlines fly an all Boeing fleet", and that is simply inaccurate.

Of the 20 largest airlines in North America, 12 are based in the US.  Of those, 3 currently operate an all-Boeing fleet (Southwest, Alaska, Sun Country), and Alaska will add Airbus planes when it acquires Virgin America.  Four others operate no Boeing aircraft (JetBlue, Frontier, Sprit, Virgin America).  The remaining five operate a mix of Boeing and non-Boeing.

"From the US is this difficult given the range of the aircraft" wikipedia claims a range of up to 6000 KM. It's not clear to me whether that is ferry range or range with a reasonable cargo, but either way it seems to be enough to make moving the aircraft between america and Europe fairly easy.


text:
What is the most recent turbofan engine that used steel for its bypass fan blades?
I haven't been able to locate any engines that use steel for the bypass fan. All sources suggest Ti and composites are used for blade construction. Apart from the weight steel could partially make up for it by offering a thinner blade, cost/ease of construction and more resistance to foreign objects.
The reason I ask is that I am trying to design a large ducted fan (800mm) that will be as cheap as possible to manufacture by using a thin sheet of stainless steel for the blade material. The cut to shape sheet will be pressed in a mold to achieve the designed AoA across the blade length and then a 3D printed airfoil will slide over it.

None of these statements are backed by evidence. Steel doesn't offer better per-volume strength but is considerably heavier than titanium. Ease of construction is marginal because it's the shape that makes things hard, not the machining characteristic of  the material.  As for resistance to foreign material, steel is probably the worst. As for cost, development cost is the big part, material cost is negotiable. Go head and do your design and make sure the math and physics checks out, so that even if it's heavy and inefficient it's at least safe.

The organisations that buy this sort of engine don't care how much it costs to make - they care about the total cost of ownership. It doesn't matter if your 'cheap' fan is half the price of the competition if the engine uses 10% more fuel. To an airline spending tens of millions per year on fuel, even 2% saving is a huge amount.

I'm curious how you will achieve enough strength by using what is basically a spar + airfoil configuration, if you make the spar out of sheet metal. Or is the 3D printed part going to be load-bearing?

Also, out of genuine curiosity: how does your cost estimate of 3D printing your blades compare to milling individual blades?

@ CatchAsCatchCan It's an electric ducted fan not meant for any sort of commercial use. The reduction in percentage points of efficiency doesn't matter as much when the range is so short anyways.

@Sanchises I'm learning as I go but the steel blade won't be flat. It will be pressed into a similar shape as seen in modern high bypass fans which will greatly increase it's load bearing capacity compared to a simple sheet of steel. The extra weight of the blade +/- 40% compared to Ti will be a downside. However, the tip speed to generate the moderate amount of thrust I need will come with much lower centrifugal forces the heavier steel blade can handle. The 3D printed airfoil will not be load bearing and will be printed out of a softer material like tpu.

@Sanchises The cost to machine a similar blade out of 7075 Aluminum would cost 100  in stock and probably 300 per blade on a 6-axis cnc. The steel sheet would be about 5  with cutting on a plasma cutter at about $10 per blade. It could also be cut on a hobby grade machine with a cutting spindle for fast prototyping.

The tickness of the Fan blade is not only defined by the structural requirement but rather for aerodynamic purpose, thus the geometry of the blade won't change much depending on the material used. Most of the metallic blades in use are hollow.
The price of the blade is quite irrelevent in modern engines. If you can decrease the wheight of the fan by 10% for double the price you'll do it as it will ensure so much fuel saving over the life of the engine. Thus I don't see the advantage of using steel over titanium for a fan blade.
Looking at other comments I understand it is for prototyping and needs to remain cheap. I would then recommend to build the core with 3D printed material which will give you the airfoil shape for aerodynamic and then enclose it with a metal sheets in order to obtain a sandwich like structure. This could greatly increase the stiffness and strength without much added weight.